Mildew smell in house

[Scott W.]

I bought a house almost 10 years ago with an odor (yep, I had it inspected); people have described the smell as musty, an old dog smell, & an old house smell. When I was dating my wife, she'd go back to her place & her clothes would smell of it.

the house is a ranch on about a 2' dirt crawl with a vapor barrier (yeah, you REALLY gotta crawl).

When the wife moved in 5 years ago, she wanted the smell gone. We hired a company to dig a french drain/sump pump, install one of those black vapor barriers, & they then cemented it.

I've read different levels of opinion as to concrete or not to concrete a crawl.

Within days, the smell was nonexistent; people who had been over before had commented on the lack of smell.

The home is now a rental; I was doing some work on it last week, with my handyman, & we both commented on the smell; it's very minor, yet noticeable upon entry.

My concern is future tentants/homebuyers will be turned off by the smell. I'm at a loss for solutions. There is a furnace humidifier as well. I'm not sure if the tentants run it though & if it would even make a difference.

Any solutions/ideas?